Merge branch '170825' of github.com:jwpi/util-linux

[thirdparty/util-linux.git] / sys-utils / hwclock.c

/*
 * hwclock.c
 *
 * clock.c was written by Charles Hedrick, hedrick@cs.rutgers.edu, Apr 1992
 * Modified for clock adjustments - Rob Hooft <hooft@chem.ruu.nl>, Nov 1992
 * Improvements by Harald Koenig <koenig@nova.tat.physik.uni-tuebingen.de>
 * and Alan Modra <alan@spri.levels.unisa.edu.au>.
 *
 * Major rewrite by Bryan Henderson <bryanh@giraffe-data.com>, 96.09.19.
 * The new program is called hwclock. New features:
 *
 *      - You can set the hardware clock without also modifying the system
 *        clock.
 *      - You can read and set the clock with finer than 1 second precision.
 *      - When you set the clock, hwclock automatically refigures the drift
 *        rate, based on how far off the clock was before you set it.
 *
 * Reshuffled things, added sparc code, and re-added alpha stuff
 * by David Mosberger <davidm@azstarnet.com>
 * and Jay Estabrook <jestabro@amt.tay1.dec.com>
 * and Martin Ostermann <ost@coments.rwth-aachen.de>, aeb@cwi.nl, 990212.
 *
 * Fix for Award 2094 bug, Dave Coffin (dcoffin@shore.net) 11/12/98
 * Change of local time handling, Stefan Ring <e9725446@stud3.tuwien.ac.at>
 * Change of adjtime handling, James P. Rutledge <ao112@rgfn.epcc.edu>.
 *
 * Distributed under GPL
 */
/*
 * Explanation of `adjusting' (Rob Hooft):
 *
 * The problem with my machine is that its CMOS clock is 10 seconds
 * per day slow. With this version of clock.c, and my '/etc/rc.local'
 * reading '/etc/clock -au' instead of '/etc/clock -u -s', this error
 * is automatically corrected at every boot.
 *
 * To do this job, the program reads and writes the file '/etc/adjtime'
 * to determine the correction, and to save its data. In this file are
 * three numbers:
 *
 *      1) the correction in seconds per day. (So if your clock runs 5
 *         seconds per day fast, the first number should read -5.0)
 *      2) the number of seconds since 1/1/1970 the last time the program
 *         was used
 *      3) the remaining part of a second which was leftover after the last
 *         adjustment
 *
 * Installation and use of this program:
 *
 *      a) create a file '/etc/adjtime' containing as the first and only
 *         line: '0.0 0 0.0'
 *      b) run 'clock -au' or 'clock -a', depending on whether your cmos is
 *         in universal or local time. This updates the second number.
 *      c) set your system time using the 'date' command.
 *      d) update your cmos time using 'clock -wu' or 'clock -w'
 *      e) replace the first number in /etc/adjtime by your correction.
 *      f) put the command 'clock -au' or 'clock -a' in your '/etc/rc.local'
 */

#include <errno.h>
#include <getopt.h>
#include <limits.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

#include "c.h"
#include "closestream.h"
#include "nls.h"
#include "optutils.h"
#include "pathnames.h"
#include "hwclock.h"
#include "timeutils.h"
#include "env.h"
#include "xalloc.h"

#ifdef HAVE_LIBAUDIT
#include <libaudit.h>
static int hwaudit_fd = -1;
#endif

/* The struct that holds our hardware access routines */
static struct clock_ops *ur;

/* Maximal clock adjustment in seconds per day.
   (adjtime() glibc call has 2145 seconds limit on i386, so it is good enough for us as well,
   43219 is a maximal safe value preventing exact_adjustment overflow.) */
#define MAX_DRIFT 2145.0

struct adjtime {
        /*
         * This is information we keep in the adjtime file that tells us how
         * to do drift corrections. Elements are all straight from the
         * adjtime file, so see documentation of that file for details.
         * Exception is <dirty>, which is an indication that what's in this
         * structure is not what's in the disk file (because it has been
         * updated since read from the disk file).
         */
        int dirty;
        /* line 1 */
        double drift_factor;
        time_t last_adj_time;
        double not_adjusted;
        /* line 2 */
        time_t last_calib_time;
        /*
         * The most recent time that we set the clock from an external
         * authority (as opposed to just doing a drift adjustment)
         */
        /* line 3 */
        enum a_local_utc { UTC = 0, LOCAL, UNKNOWN } local_utc;
        /*
         * To which time zone, local or UTC, we most recently set the
         * hardware clock.
         */
};

/*
 * time_t to timeval conversion.
 */
static struct timeval t2tv(time_t timet)
{
        struct timeval rettimeval;

        rettimeval.tv_sec = timet;
        rettimeval.tv_usec = 0;
        return rettimeval;
}

/*
 * The difference in seconds between two times in "timeval" format.
 */
double time_diff(struct timeval subtrahend, struct timeval subtractor)
{
        return (subtrahend.tv_sec - subtractor.tv_sec)
            + (subtrahend.tv_usec - subtractor.tv_usec) / 1E6;
}

/*
 * The time, in "timeval" format, which is <increment> seconds after the
 * time <addend>. Of course, <increment> may be negative.
 */
static struct timeval time_inc(struct timeval addend, double increment)
{
        struct timeval newtime;

        newtime.tv_sec = addend.tv_sec + (int)increment;
        newtime.tv_usec = addend.tv_usec + (increment - (int)increment) * 1E6;

        /*
         * Now adjust it so that the microsecond value is between 0 and 1
         * million.
         */
        if (newtime.tv_usec < 0) {
                newtime.tv_usec += 1E6;
                newtime.tv_sec -= 1;
        } else if (newtime.tv_usec >= 1E6) {
                newtime.tv_usec -= 1E6;
                newtime.tv_sec += 1;
        }
        return newtime;
}

static int
hw_clock_is_utc(const struct hwclock_control *ctl,
                const struct adjtime adjtime)
{
        int ret;

        if (ctl->utc)
                ret = 1;        /* --utc explicitly given on command line */
        else if (ctl->local_opt)
                ret = 0;        /* --localtime explicitly given */
        else
                /* get info from adjtime file - default is UTC */
                ret = (adjtime.local_utc != LOCAL);
        if (ctl->debug)
                printf(_("Assuming hardware clock is kept in %s time.\n"),
                       ret ? _("UTC") : _("local"));
        return ret;
}

/*
 * Read the adjustment parameters out of the /etc/adjtime file.
 *
 * Return them as the adjtime structure <*adjtime_p>. Its defaults are
 * initialized in main().
 */
static int read_adjtime(const struct hwclock_control *ctl,
                        struct adjtime *adjtime_p)
{
        FILE *adjfile;
        char line1[81];         /* String: first line of adjtime file */
        char line2[81];         /* String: second line of adjtime file */
        char line3[81];         /* String: third line of adjtime file */

        if (access(ctl->adj_file_name, R_OK) != 0)
                return EXIT_SUCCESS;

        adjfile = fopen(ctl->adj_file_name, "r");       /* open file for reading */
        if (adjfile == NULL) {
                warn(_("cannot open %s"), ctl->adj_file_name);
                return EXIT_FAILURE;
        }

        if (!fgets(line1, sizeof(line1), adjfile))
                line1[0] = '\0';        /* In case fgets fails */
        if (!fgets(line2, sizeof(line2), adjfile))
                line2[0] = '\0';        /* In case fgets fails */
        if (!fgets(line3, sizeof(line3), adjfile))
                line3[0] = '\0';        /* In case fgets fails */

        fclose(adjfile);

        sscanf(line1, "%lf %ld %lf",
               &adjtime_p->drift_factor,
               &adjtime_p->last_adj_time,
               &adjtime_p->not_adjusted);

        sscanf(line2, "%ld", &adjtime_p->last_calib_time);

        if (!strcmp(line3, "UTC\n")) {
                adjtime_p->local_utc = UTC;
        } else if (!strcmp(line3, "LOCAL\n")) {
                adjtime_p->local_utc = LOCAL;
        } else {
                adjtime_p->local_utc = UNKNOWN;
                if (line3[0]) {
                        warnx(_("Warning: unrecognized third line in adjtime file\n"
                                "(Expected: `UTC' or `LOCAL' or nothing.)"));
                }
        }

        if (ctl->debug) {
                printf(_
                       ("Last drift adjustment done at %ld seconds after 1969\n"),
                       (long)adjtime_p->last_adj_time);
                printf(_("Last calibration done at %ld seconds after 1969\n"),
                       (long)adjtime_p->last_calib_time);
                printf(_("Hardware clock is on %s time\n"),
                       (adjtime_p->local_utc ==
                        LOCAL) ? _("local") : (adjtime_p->local_utc ==
                                               UTC) ? _("UTC") : _("unknown"));
        }

        return EXIT_SUCCESS;
}

/*
 * Wait until the falling edge of the Hardware Clock's update flag so that
 * any time that is read from the clock immediately after we return will be
 * exact.
 *
 * The clock only has 1 second precision, so it gives the exact time only
 * once per second, right on the falling edge of the update flag.
 *
 * We wait (up to one second) either blocked waiting for an rtc device or in
 * a CPU spin loop. The former is probably not very accurate.
 *
 * Return 0 if it worked, nonzero if it didn't.
 */
static int synchronize_to_clock_tick(const struct hwclock_control *ctl)
{
        int rc;

        if (ctl->debug)
                printf(_("Waiting for clock tick...\n"));

        rc = ur->synchronize_to_clock_tick(ctl);

        if (ctl->debug) {
                if (rc)
                        printf(_("...synchronization failed\n"));
                else
                        printf(_("...got clock tick\n"));
        }

        return rc;
}

/*
 * Convert a time in broken down format (hours, minutes, etc.) into standard
 * unix time (seconds into epoch). Return it as *systime_p.
 *
 * The broken down time is argument <tm>. This broken down time is either
 * in local time zone or UTC, depending on value of logical argument
 * "universal". True means it is in UTC.
 *
 * If the argument contains values that do not constitute a valid time, and
 * mktime() recognizes this, return *valid_p == false and *systime_p
 * undefined. However, mktime() sometimes goes ahead and computes a
 * fictional time "as if" the input values were valid, e.g. if they indicate
 * the 31st day of April, mktime() may compute the time of May 1. In such a
 * case, we return the same fictional value mktime() does as *systime_p and
 * return *valid_p == true.
 */
static int
mktime_tz(const struct hwclock_control *ctl, struct tm tm,
          time_t *systime_p)
{
        int valid;

        if (ctl->universal)
                *systime_p = timegm(&tm);
        else
                *systime_p = mktime(&tm);
        if (*systime_p == -1) {
                /*
                 * This apparently (not specified in mktime() documentation)
                 * means the 'tm' structure does not contain valid values
                 * (however, not containing valid values does _not_ imply
                 * mktime() returns -1).
                 */
                valid = 0;
                if (ctl->debug)
                        printf(_("Invalid values in hardware clock: "
                                 "%4d/%.2d/%.2d %.2d:%.2d:%.2d\n"),
                               tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
                               tm.tm_hour, tm.tm_min, tm.tm_sec);
        } else {
                valid = 1;
                if (ctl->debug)
                        printf(_
                               ("Hw clock time : %4d/%.2d/%.2d %.2d:%.2d:%.2d = "
                                "%ld seconds since 1969\n"), tm.tm_year + 1900,
                               tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min,
                               tm.tm_sec, (long)*systime_p);
        }
        return valid;
}

/*
 * Read the hardware clock and return the current time via <tm> argument.
 *
 * Use the method indicated by <method> argument to access the hardware
 * clock.
 */
static int
read_hardware_clock(const struct hwclock_control *ctl,
                    int *valid_p, time_t *systime_p)
{
        struct tm tm;
        int err;

        err = ur->read_hardware_clock(ctl, &tm);
        if (err)
                return err;

        if (ctl->debug)
                printf(_
                       ("Time read from Hardware Clock: %4d/%.2d/%.2d %02d:%02d:%02d\n"),
                       tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour,
                       tm.tm_min, tm.tm_sec);
        *valid_p = mktime_tz(ctl, tm, systime_p);

        return 0;
}

/*
 * Set the Hardware Clock to the time <newtime>, in local time zone or UTC,
 * according to <universal>.
 */
static void
set_hardware_clock(const struct hwclock_control *ctl, const time_t newtime)
{
        struct tm new_broken_time;
        /*
         * Time to which we will set Hardware Clock, in broken down format,
         * in the time zone of caller's choice
         */

        if (ctl->universal)
                new_broken_time = *gmtime(&newtime);
        else
                new_broken_time = *localtime(&newtime);

        if (ctl->debug)
                printf(_("Setting Hardware Clock to %.2d:%.2d:%.2d "
                         "= %ld seconds since 1969\n"),
                       new_broken_time.tm_hour, new_broken_time.tm_min,
                       new_broken_time.tm_sec, (long)newtime);

        if (ctl->testing)
                printf(_("Test mode: clock was not changed\n"));
        else
                ur->set_hardware_clock(ctl, &new_broken_time);
}

/*
 * Set the Hardware Clock to the time "sethwtime", in local time zone or
 * UTC, according to "universal".
 *
 * Wait for a fraction of a second so that "sethwtime" is the value of the
 * Hardware Clock as of system time "refsystime", which is in the past. For
 * example, if "sethwtime" is 14:03:05 and "refsystime" is 12:10:04.5 and
 * the current system time is 12:10:06.0: Wait .5 seconds (to make exactly 2
 * seconds since "refsystime") and then set the Hardware Clock to 14:03:07,
 * thus getting a precise and retroactive setting of the clock.
 *
 * (Don't be confused by the fact that the system clock and the Hardware
 * Clock differ by two hours in the above example. That's just to remind you
 * that there are two independent time scales here).
 *
 * This function ought to be able to accept set times as fractional times.
 * Idea for future enhancement.
 */
static void
set_hardware_clock_exact(const struct hwclock_control *ctl,
                         const time_t sethwtime,
                         const struct timeval refsystime)
{
        /*
         * The Hardware Clock can only be set to any integer time plus one
         * half second.  The integer time is required because there is no
         * interface to set or get a fractional second.  The additional half
         * second is because the Hardware Clock updates to the following
         * second precisely 500 ms (not 1 second!) after you release the
         * divider reset (after setting the new time) - see description of
         * DV2, DV1, DV0 in Register A in the MC146818A data sheet (and note
         * that although that document doesn't say so, real-world code seems
         * to expect that the SET bit in Register B functions the same way).
         * That means that, e.g., when you set the clock to 1:02:03, it
         * effectively really sets it to 1:02:03.5, because it will update to
         * 1:02:04 only half a second later.  Our caller passes the desired
         * integer Hardware Clock time in sethwtime, and the corresponding
         * system time (which may have a fractional part, and which may or may
         * not be the same!) in refsystime.  In an ideal situation, we would
         * then apply sethwtime to the Hardware Clock at refsystime+500ms, so
         * that when the Hardware Clock ticks forward to sethwtime+1s half a
         * second later at refsystime+1000ms, everything is in sync.  So we
         * spin, waiting for gettimeofday() to return a time at or after that
         * time (refsystime+500ms) up to a tolerance value, initially 1ms.  If
         * we miss that time due to being preempted for some other process,
         * then we increase the margin a little bit (initially 1ms, doubling
         * each time), add 1 second (or more, if needed to get a time that is
         * in the future) to both the time for which we are waiting and the
         * time that we will apply to the Hardware Clock, and start waiting
         * again.
         * 
         * For example, the caller requests that we set the Hardware Clock to
         * 1:02:03, with reference time (current system time) = 6:07:08.250.
         * We want the Hardware Clock to update to 1:02:04 at 6:07:09.250 on
         * the system clock, and the first such update will occur 0.500
         * seconds after we write to the Hardware Clock, so we spin until the
         * system clock reads 6:07:08.750.  If we get there, great, but let's
         * imagine the system is so heavily loaded that our process is
         * preempted and by the time we get to run again, the system clock
         * reads 6:07:11.990.  We now want to wait until the next xx:xx:xx.750
         * time, which is 6:07:12.750 (4.5 seconds after the reference time),
         * at which point we will set the Hardware Clock to 1:02:07 (4 seconds
         * after the originally requested time).  If we do that successfully,
         * then at 6:07:13.250 (5 seconds after the reference time), the
         * Hardware Clock will update to 1:02:08 (5 seconds after the
         * originally requested time), and all is well thereafter.
         */

        time_t newhwtime = sethwtime;
        double target_time_tolerance_secs = 0.001;  /* initial value */
        double tolerance_incr_secs = 0.001;         /* initial value */
        const double RTC_SET_DELAY_SECS = 0.5;      /* 500 ms */
        const struct timeval RTC_SET_DELAY_TV = { 0, RTC_SET_DELAY_SECS * 1E6 };

        struct timeval targetsystime;
        struct timeval nowsystime;
        struct timeval prevsystime = refsystime;
        double deltavstarget;

        timeradd(&refsystime, &RTC_SET_DELAY_TV, &targetsystime);

        while (1) {
                double ticksize;

                /* FOR TESTING ONLY: inject random delays of up to 1000ms */
                if (ctl->debug >= 10) {
                        int usec = random() % 1000000;
                        printf(_("sleeping ~%d usec\n"), usec);
                        xusleep(usec);
                }

                gettimeofday(&nowsystime, NULL);
                deltavstarget = time_diff(nowsystime, targetsystime);
                ticksize = time_diff(nowsystime, prevsystime);
                prevsystime = nowsystime;

                if (ticksize < 0) {
                        if (ctl->debug)
                                printf(_("time jumped backward %.6f seconds "
                                         "to %ld.%06ld - retargeting\n"),
                                       ticksize, nowsystime.tv_sec,
                                       nowsystime.tv_usec);
                        /* The retarget is handled at the end of the loop. */
                } else if (deltavstarget < 0) {
                        /* deltavstarget < 0 if current time < target time */
                        if (ctl->debug >= 2)
                                printf(_("%ld.%06ld < %ld.%06ld (%.6f)\n"),
                                       nowsystime.tv_sec,
                                       nowsystime.tv_usec,
                                       targetsystime.tv_sec,
                                       targetsystime.tv_usec,
                                       deltavstarget);
                        continue;  /* not there yet - keep spinning */
                } else if (deltavstarget <= target_time_tolerance_secs) {
                        /* Close enough to the target time; done waiting. */
                        break;
                } else /* (deltavstarget > target_time_tolerance_secs) */ {
                        /*
                         * We missed our window.  Increase the tolerance and
                         * aim for the next opportunity.
                         */
                        if (ctl->debug)
                                printf(_("missed it - %ld.%06ld is too far "
                                         "past %ld.%06ld (%.6f > %.6f)\n"),
                                       nowsystime.tv_sec,
                                       nowsystime.tv_usec,
                                       targetsystime.tv_sec,
                                       targetsystime.tv_usec,
                                       deltavstarget,
                                       target_time_tolerance_secs);
                        target_time_tolerance_secs += tolerance_incr_secs;
                        tolerance_incr_secs *= 2;
                }

                /*
                 * Aim for the same offset (tv_usec) within the second in
                 * either the current second (if that offset hasn't arrived
                 * yet), or the next second.
                 */
                if (nowsystime.tv_usec < targetsystime.tv_usec)
                        targetsystime.tv_sec = nowsystime.tv_sec;
                else
                        targetsystime.tv_sec = nowsystime.tv_sec + 1;
        }

        newhwtime = sethwtime
                    + (int)(time_diff(nowsystime, refsystime)
                            - RTC_SET_DELAY_SECS /* don't count this */
                            + 0.5 /* for rounding */);
        if (ctl->debug)
                printf(_("%ld.%06ld is close enough to %ld.%06ld (%.6f < %.6f)\n"
                         "Set RTC to %ld (%ld + %d; refsystime = %ld.%06ld)\n"),
                       nowsystime.tv_sec, nowsystime.tv_usec,
                       targetsystime.tv_sec, targetsystime.tv_usec,
                       deltavstarget, target_time_tolerance_secs,
                       newhwtime, sethwtime,
                       (int)(newhwtime - sethwtime),
                       refsystime.tv_sec, refsystime.tv_usec);

        set_hardware_clock(ctl, newhwtime);
}

static void
display_time(struct timeval hwctime)
{
        char buf[ISO_8601_BUFSIZ];

        strtimeval_iso(&hwctime, ISO_8601_DATE|ISO_8601_TIME|ISO_8601_DOTUSEC|
                                 ISO_8601_TIMEZONE|ISO_8601_SPACE,
                                 buf, sizeof(buf));
        printf("%s\n", buf);
}

/*
 * Adjusts System time, sets the kernel's timezone and RTC timescale.
 *
 * The kernel warp_clock function adjusts the System time according to the
 * tz.tz_minuteswest argument and sets PCIL (see below). At boot settimeofday(2)
 * has one-shot access to this function as shown in the table below.
 *
 * +-------------------------------------------------------------------+
 * |                       settimeofday(tv, tz)                        |
 * |-------------------------------------------------------------------|
 * |     Arguments     |  System Time  | PCIL |           | warp_clock |
 * |   tv    |   tz    | set  | warped | set  | firsttime |   locked   |
 * |---------|---------|---------------|------|-----------|------------|
 * | pointer | NULL    |  yes |   no   |  no  |     1     |    no      |
 * | pointer | pointer |  yes |   no   |  no  |     0     |    yes     |
 * | NULL    | ptr2utc |  no  |   no   |  no  |     0     |    yes     |
 * | NULL    | pointer |  no  |   yes  |  yes |     0     |    yes     |
 * +-------------------------------------------------------------------+
 * ptr2utc: tz.tz_minuteswest is zero (UTC).
 * PCIL: persistent_clock_is_local, sets the "11 minute mode" timescale.
 * firsttime: locks the warp_clock function (initialized to 1 at boot).
 *
 * +---------------------------------------------------------------------------+
 * |  op     | RTC scale | settimeofday calls                                  |
 * |---------|-----------|-----------------------------------------------------|
 * | systz   |   Local   | 1) warps system time*, sets PCIL* and kernel tz     |
 * | systz   |   UTC     | 1st) locks warp_clock* 2nd) sets kernel tz          |
 * | hctosys |   Local   | 1st) sets PCIL* 2nd) sets system time and kernel tz |
 * | hctosys |   UTC     | 1) sets system time and kernel tz                   |
 * +---------------------------------------------------------------------------+
 *                         * only on first call after boot
 */
static int
set_system_clock(const struct hwclock_control *ctl,
                 const struct timeval newtime)
{
        struct tm *broken;
        int minuteswest;
        int rc = 0;
        const struct timezone tz_utc = { 0 };

        broken = localtime(&newtime.tv_sec);
#ifdef HAVE_TM_GMTOFF
        minuteswest = -broken->tm_gmtoff / 60;  /* GNU extension */
#else
        minuteswest = timezone / 60;
        if (broken->tm_isdst)
                minuteswest -= 60;
#endif

        if (ctl->debug) {
                if (ctl->hctosys && !ctl->universal)
                        printf(_("Calling settimeofday(NULL, %d) to set "
                                 "persistent_clock_is_local.\n"), minuteswest);
                if (ctl->systz && ctl->universal)
                        puts(_("Calling settimeofday(NULL, 0) "
                                "to lock the warp function."));
                if (ctl->hctosys)
                        printf(_("Calling settimeofday(%ld.%06ld, %d)\n"),
                               newtime.tv_sec, newtime.tv_usec, minuteswest);
                else {
                        printf(_("Calling settimeofday(NULL, %d) "), minuteswest);
                        if (ctl->universal)
                                 puts(_("to set the kernel timezone."));
                        else
                                 puts(_("to warp System time."));
                }
        }

        if (ctl->testing) {
                printf(_
                       ("Test mode: clock was not changed\n"));
        } else {
                const struct timezone tz = { minuteswest };

                if (ctl->hctosys && !ctl->universal)    /* set PCIL */
                        rc = settimeofday(NULL, &tz);
                if (ctl->systz && ctl->universal)       /* lock warp_clock */
                        rc = settimeofday(NULL, &tz_utc);
                if (!rc && ctl->hctosys)
                        rc = settimeofday(&newtime, &tz);
                else if (!rc)
                        rc = settimeofday(NULL, &tz);

                if (rc) {
                        warn(_("settimeofday() failed"));
                        return  EXIT_FAILURE;
                }
        }
        return EXIT_SUCCESS;
}

/*
 * Refresh the last calibrated and last adjusted timestamps in <*adjtime_p>
 * to facilitate future drift calculations based on this set point.
 *
 * With the --update-drift option:
 * Update the drift factor in <*adjtime_p> based on the fact that the
 * Hardware Clock was just calibrated to <nowtime> and before that was
 * set to the <hclocktime> time scale.
 */
static void
adjust_drift_factor(const struct hwclock_control *ctl,
                    struct adjtime *adjtime_p,
                    const struct timeval nowtime,
                    const struct timeval hclocktime)
{
        if (!ctl->update) {
                if (ctl->debug)
                        printf(_("Not adjusting drift factor because the "
                                 "--update-drift option was not used.\n"));
        } else if (adjtime_p->last_calib_time == 0) {
                if (ctl->debug)
                        printf(_("Not adjusting drift factor because last "
                                 "calibration time is zero,\n"
                                 "so history is bad and calibration startover "
                                 "is necessary.\n"));
        } else if ((hclocktime.tv_sec - adjtime_p->last_calib_time) < 4 * 60 * 60) {
                if (ctl->debug)
                        printf(_("Not adjusting drift factor because it has "
                                 "been less than four hours since the last "
                                 "calibration.\n"));
        } else {
                /*
                 * At adjustment time we drift correct the hardware clock
                 * according to the contents of the adjtime file and refresh
                 * its last adjusted timestamp.
                 *
                 * At calibration time we set the Hardware Clock and refresh
                 * both timestamps in <*adjtime_p>.
                 *
                 * Here, with the --update-drift option, we also update the
                 * drift factor in <*adjtime_p>.
                 *
                 * Let us do computation in doubles. (Floats almost suffice,
                 * but 195 days + 1 second equals 195 days in floats.)
                 */
                const double sec_per_day = 24.0 * 60.0 * 60.0;
                double factor_adjust;
                double drift_factor;
                struct timeval last_calib;

                last_calib = t2tv(adjtime_p->last_calib_time);
                /*
                 * Correction to apply to the current drift factor.
                 *
                 * Simplified: uncorrected_drift / days_since_calibration.
                 *
                 * hclocktime is fully corrected with the current drift factor.
                 * Its difference from nowtime is the missed drift correction.
                 */
                factor_adjust = time_diff(nowtime, hclocktime) /
                                (time_diff(nowtime, last_calib) / sec_per_day);

                drift_factor = adjtime_p->drift_factor + factor_adjust;
                if (fabs(drift_factor) > MAX_DRIFT) {
                        if (ctl->debug)
                                printf(_("Clock drift factor was calculated as "
                                         "%f seconds/day.\n"
                                         "It is far too much. Resetting to zero.\n"),
                                       drift_factor);
                        drift_factor = 0;
                } else {
                        if (ctl->debug)
                                printf(_("Clock drifted %f seconds in the past "
                                         "%f seconds\nin spite of a drift factor of "
                                         "%f seconds/day.\n"
                                         "Adjusting drift factor by %f seconds/day\n"),
                                       time_diff(nowtime, hclocktime),
                                       time_diff(nowtime, last_calib),
                                       adjtime_p->drift_factor, factor_adjust);
                }

                adjtime_p->drift_factor = drift_factor;
        }
        adjtime_p->last_calib_time = nowtime.tv_sec;

        adjtime_p->last_adj_time = nowtime.tv_sec;

        adjtime_p->not_adjusted = 0;

        adjtime_p->dirty = 1;
}

/*
 * Calculate the drift correction currently needed for the
 * Hardware Clock based on the last time it was adjusted,
 * and the current drift factor, as stored in the adjtime file.
 *
 * The total drift adjustment needed is stored at tdrift_p.
 *
 */
static void
calculate_adjustment(const struct hwclock_control *ctl,
                     const double factor,
                     const time_t last_time,
                     const double not_adjusted,
                     const time_t systime, struct timeval *tdrift_p)
{
        double exact_adjustment;

        exact_adjustment =
            ((double)(systime - last_time)) * factor / (24 * 60 * 60)
            + not_adjusted;
        tdrift_p->tv_sec = (time_t) floor(exact_adjustment);
        tdrift_p->tv_usec = (exact_adjustment -
                                 (double)tdrift_p->tv_sec) * 1E6;
        if (ctl->debug) {
                printf(P_("Time since last adjustment is %ld second\n",
                        "Time since last adjustment is %ld seconds\n",
                       (systime - last_time)),
                       (systime - last_time));
                printf(_("Calculated Hardware Clock drift is %ld.%06ld seconds\n"),
                       tdrift_p->tv_sec, tdrift_p->tv_usec);
        }
}

/*
 * Write the contents of the <adjtime> structure to its disk file.
 *
 * But if the contents are clean (unchanged since read from disk), don't
 * bother.
 */
static void save_adjtime(const struct hwclock_control *ctl,
                         const struct adjtime *adjtime)
{
        char *content;          /* Stuff to write to disk file */
        FILE *fp;
        int err = 0;

        if (!adjtime->dirty)
                return;

        xasprintf(&content, "%f %ld %f\n%ld\n%s\n",
                  adjtime->drift_factor,
                  adjtime->last_adj_time,
                  adjtime->not_adjusted,
                  adjtime->last_calib_time,
                  (adjtime->local_utc == LOCAL) ? "LOCAL" : "UTC");

        if (ctl->testing) {
                if (ctl->debug){
                        printf(_("Test mode: %s was not updated with:\n%s"),
                               ctl->adj_file_name, content);
                }
                free(content);
                return;
        }

        fp = fopen(ctl->adj_file_name, "w");
        if (fp == NULL) {
                warn(_("Could not open file with the clock adjustment parameters "
                       "in it (%s) for writing"), ctl->adj_file_name);
                err = 1;
        } else if (fputs(content, fp) < 0 || close_stream(fp) != 0) {
                warn(_("Could not update file with the clock adjustment "
                       "parameters (%s) in it"), ctl->adj_file_name);
                err = 1;
        }
        free(content);
        if (err)
                warnx(_("Drift adjustment parameters not updated."));
}

/*
 * Do the adjustment requested, by 1) setting the Hardware Clock (if
 * necessary), and 2) updating the last-adjusted time in the adjtime
 * structure.
 *
 * Do not update anything if the Hardware Clock does not currently present a
 * valid time.
 *
 * <hclocktime> is the drift corrected time read from the Hardware Clock.
 *
 * <read_time> was the system time when the <hclocktime> was read, which due
 * to computational delay could be a short time ago. It is used to define a
 * trigger point for setting the Hardware Clock. The fractional part of the
 * Hardware clock set time is subtracted from read_time to 'refer back', or
 * delay, the trigger point.  Fractional parts must be accounted for in this
 * way, because the Hardware Clock can only be set to a whole second.
 *
 * <universal>: the Hardware Clock is kept in UTC.
 *
 * <testing>:  We are running in test mode (no updating of clock).
 *
 */
static void
do_adjustment(const struct hwclock_control *ctl, struct adjtime *adjtime_p,
              const struct timeval hclocktime,
              const struct timeval read_time)
{
        if (adjtime_p->last_adj_time == 0) {
                if (ctl->debug)
                        printf(_("Not setting clock because last adjustment time is zero, "
                                 "so history is bad.\n"));
        } else if (fabs(adjtime_p->drift_factor) > MAX_DRIFT) {
                if (ctl->debug)
                        printf(_("Not setting clock because drift factor %f is far too high.\n"),
                                adjtime_p->drift_factor);
        } else {
                set_hardware_clock_exact(ctl, hclocktime.tv_sec,
                                         time_inc(read_time,
                                                  -(hclocktime.tv_usec / 1E6)));
                adjtime_p->last_adj_time = hclocktime.tv_sec;
                adjtime_p->not_adjusted = 0;
                adjtime_p->dirty = 1;
        }
}

static void determine_clock_access_method(const struct hwclock_control *ctl)
{
        ur = NULL;

        if (ctl->directisa)
                ur = probe_for_cmos_clock();
#ifdef __linux__
        if (!ur)
                ur = probe_for_rtc_clock(ctl);
#endif
        if (ur) {
                if (ctl->debug)
                        puts(ur->interface_name);

        } else {
                if (ctl->debug)
                        printf(_("No usable clock interface found.\n"));
                warnx(_("Cannot access the Hardware Clock via "
                        "any known method."));
                if (!ctl->debug)
                        warnx(_("Use the --debug option to see the "
                                "details of our search for an access "
                                "method."));
                hwclock_exit(ctl, EXIT_FAILURE);
        }
}

/* Do all the normal work of hwclock - read, set clock, etc. */
static int
manipulate_clock(const struct hwclock_control *ctl, const time_t set_time,
                 const struct timeval startup_time, struct adjtime *adjtime)
{
        /* The time at which we read the Hardware Clock */
        struct timeval read_time;
        /*
         * The Hardware Clock gives us a valid time, or at
         * least something close enough to fool mktime().
         */
        int hclock_valid = 0;
        /*
         * Tick synchronized time read from the Hardware Clock and
         * then drift corrected for all operations except --show.
         */
        struct timeval hclocktime = { 0 };
        /*
         * hclocktime correlated to startup_time. That is, what drift
         * corrected Hardware Clock time would have been at start up.
         */
        struct timeval startup_hclocktime = { 0 };
        /* Total Hardware Clock drift correction needed. */
        struct timeval tdrift;

        if ((ctl->set || ctl->systohc || ctl->adjust) &&
            (adjtime->local_utc == UTC) != ctl->universal) {
                adjtime->local_utc = ctl->universal ? UTC : LOCAL;
                adjtime->dirty = 1;
        }
        /*
         * Negate the drift correction, because we want to 'predict' a
         * Hardware Clock time that includes drift.
         */
        if (ctl->predict) {
                hclocktime = t2tv(set_time);
                calculate_adjustment(ctl, adjtime->drift_factor,
                                     adjtime->last_adj_time,
                                     adjtime->not_adjusted,
                                     hclocktime.tv_sec, &tdrift);
                hclocktime = time_inc(hclocktime, (double)
                                      -(tdrift.tv_sec + tdrift.tv_usec / 1E6));
                if (ctl->debug) {
                        printf(_ ("Target date:   %ld\n"), set_time);
                        printf(_ ("Predicted RTC: %ld\n"), hclocktime.tv_sec);
                }
                display_time(hclocktime);
                return EXIT_SUCCESS;
        }

        if (ctl->systz)
                return set_system_clock(ctl, startup_time);

        if (ur->get_permissions())
                return EXIT_FAILURE;

        /*
         * Read and drift correct RTC time; except for RTC set functions
         * without the --update-drift option because: 1) it's not needed;
         * 2) it enables setting a corrupted RTC without reading it first;
         * 3) it significantly reduces system shutdown time.
         */
        if ( ! ((ctl->set || ctl->systohc) && !ctl->update)) {
                /*
                 * Timing critical - do not change the order of, or put
                 * anything between the follow three statements.
                 * Synchronization failure MUST exit, because all drift
                 * operations are invalid without it.
                 */
                if (synchronize_to_clock_tick(ctl))
                        return EXIT_FAILURE;
                read_hardware_clock(ctl, &hclock_valid, &hclocktime.tv_sec);
                gettimeofday(&read_time, NULL);

                if (!hclock_valid) {
                        warnx(_("RTC read returned an invalid value."));
                        return EXIT_FAILURE;
                }
                /*
                 * Calculate and apply drift correction to the Hardware Clock
                 * time for everything except --show
                 */
                calculate_adjustment(ctl, adjtime->drift_factor,
                                     adjtime->last_adj_time,
                                     adjtime->not_adjusted,
                                     hclocktime.tv_sec, &tdrift);
                if (!ctl->show)
                        hclocktime = time_inc(tdrift, hclocktime.tv_sec);

                startup_hclocktime =
                 time_inc(hclocktime, time_diff(startup_time, read_time));
        }
        if (ctl->show || ctl->get) {
                display_time(startup_hclocktime);
        } else if (ctl->set) {
                set_hardware_clock_exact(ctl, set_time, startup_time);
                if (!ctl->noadjfile)
                        adjust_drift_factor(ctl, adjtime, t2tv(set_time),
                                            startup_hclocktime);
        } else if (ctl->adjust) {
                if (tdrift.tv_sec > 0 || tdrift.tv_sec < -1)
                        do_adjustment(ctl, adjtime, hclocktime, read_time);
                else
                        printf(_("Needed adjustment is less than one second, "
                                 "so not setting clock.\n"));
        } else if (ctl->systohc) {
                struct timeval nowtime, reftime;
                /*
                 * We can only set_hardware_clock_exact to a
                 * whole seconds time, so we set it with
                 * reference to the most recent whole
                 * seconds time.
                 */
                gettimeofday(&nowtime, NULL);
                reftime.tv_sec = nowtime.tv_sec;
                reftime.tv_usec = 0;
                set_hardware_clock_exact(ctl, (time_t) reftime.tv_sec, reftime);
                if (!ctl->noadjfile)
                        adjust_drift_factor(ctl, adjtime, nowtime,
                                            hclocktime);
        } else if (ctl->hctosys) {
                return set_system_clock(ctl, hclocktime);
        }
        if (!ctl->noadjfile)
                save_adjtime(ctl, adjtime);
        return EXIT_SUCCESS;
}

/**
 * Get or set the kernel RTC driver's epoch on Alpha machines.
 * ISA machines are hard coded for 1900.
 */
#if defined(__linux__) && defined(__alpha__)
static void
manipulate_epoch(const struct hwclock_control *ctl)
{
        if (ctl->getepoch) {
                unsigned long epoch;

                if (get_epoch_rtc(ctl, &epoch))
                        warnx(_("unable to read the RTC epoch."));
                else
                        printf(_("The RTC epoch is set to %lu.\n"), epoch);
        } else if (ctl->setepoch) {
                if (!ctl->epoch_option)
                        warnx(_("--epoch is required for --setepoch."));
                else if (ctl->testing)
                        printf(_("Test mode: epoch was not set to %s.\n"),
                               ctl->epoch_option);
                else if (set_epoch_rtc(ctl))
                        warnx(_("unable to set the RTC epoch."));
        }
}
#endif          /* __linux__ __alpha__ */

static void out_version(void)
{
        printf(UTIL_LINUX_VERSION);
}

static void __attribute__((__noreturn__))
usage(void)
{
        fputs(USAGE_HEADER, stdout);
        printf(_(" %s [function] [option...]\n"), program_invocation_short_name);

        fputs(USAGE_SEPARATOR, stdout);
        puts(_("Time clocks utility."));

        fputs(USAGE_FUNCTIONS, stdout);
        puts(_(" -r, --show           display the RTC time"));
        puts(_("     --get            display drift corrected RTC time"));
        puts(_("     --set            set the RTC according to --date"));
        puts(_(" -s, --hctosys        set the system time from the RTC"));
        puts(_(" -w, --systohc        set the RTC from the system time"));
        puts(_("     --systz          send timescale configurations to the kernel"));
        puts(_("     --adjust         adjust the RTC to account for systematic drift"));
#if defined(__linux__) && defined(__alpha__)
        puts(_("     --getepoch       display the RTC epoch"));
        puts(_("     --setepoch       set the RTC epoch according to --epoch"));
#endif
        puts(_("     --predict        predict the drifted RTC time according to --date"));
        fputs(USAGE_OPTIONS, stdout);
        puts(_(" -u, --utc            the RTC timescale is UTC"));
        puts(_(" -l, --localtime      the RTC timescale is Local"));
#ifdef __linux__
        printf(_(
               " -f, --rtc <file>     use an alternate file to %1$s\n"), _PATH_RTC_DEV);
#endif
        printf(_(
               "     --directisa      use the ISA bus instead of %1$s access\n"), _PATH_RTC_DEV);
        puts(_("     --date <time>    date/time input for --set and --predict"));
#if defined(__linux__) && defined(__alpha__)
        puts(_("     --epoch <year>   epoch input for --setepoch"));
#endif
        puts(_("     --update-drift   update the RTC drift factor"));
        printf(_(
               "     --noadjfile      do not use %1$s\n"), _PATH_ADJTIME);
        printf(_(
               "     --adjfile <file> use an alternate file to %1$s\n"), _PATH_ADJTIME);
        puts(_("     --test           dry run; use -D to view what would have happened"));
        puts(_(" -D, --debug          use debug mode"));
        fputs(USAGE_SEPARATOR, stdout);
        printf(USAGE_HELP_OPTIONS(22));
        printf(USAGE_MAN_TAIL("hwclock(8)"));
        exit(EXIT_SUCCESS);
}

int main(int argc, char **argv)
{
        struct hwclock_control ctl = { .show = 1 }; /* default op is show */
        struct timeval startup_time;
        struct adjtime adjtime = { 0 };
        struct timespec when = { 0 };
        /*
         * The time we started up, in seconds into the epoch, including
         * fractions.
         */
        time_t set_time = 0;    /* Time to which user said to set Hardware Clock */
        int rc, c;

        /* Long only options. */
        enum {
                OPT_ADJFILE = CHAR_MAX + 1,
                OPT_DATE,
                OPT_DIRECTISA,
                OPT_EPOCH,
                OPT_GET,
                OPT_GETEPOCH,
                OPT_NOADJFILE,
                OPT_PREDICT,
                OPT_SET,
                OPT_SETEPOCH,
                OPT_SYSTZ,
                OPT_TEST,
                OPT_UPDATE
        };

        static const struct option longopts[] = {
                { "adjust",       no_argument,       NULL, 'a'            },
                { "help",         no_argument,       NULL, 'h'            },
                { "localtime",    no_argument,       NULL, 'l'            },
                { "show",         no_argument,       NULL, 'r'            },
                { "hctosys",      no_argument,       NULL, 's'            },
                { "utc",          no_argument,       NULL, 'u'            },
                { "version",      no_argument,       NULL, 'v'            },
                { "systohc",      no_argument,       NULL, 'w'            },
                { "debug",        no_argument,       NULL, 'D'            },
                { "set",          no_argument,       NULL, OPT_SET        },
#if defined(__linux__) && defined(__alpha__)
                { "getepoch",     no_argument,       NULL, OPT_GETEPOCH   },
                { "setepoch",     no_argument,       NULL, OPT_SETEPOCH   },
                { "epoch",        required_argument, NULL, OPT_EPOCH      },
#endif
                { "noadjfile",    no_argument,       NULL, OPT_NOADJFILE  },
                { "directisa",    no_argument,       NULL, OPT_DIRECTISA  },
                { "test",         no_argument,       NULL, OPT_TEST       },
                { "date",         required_argument, NULL, OPT_DATE       },
#ifdef __linux__
                { "rtc",          required_argument, NULL, 'f'            },
#endif
                { "adjfile",      required_argument, NULL, OPT_ADJFILE    },
                { "systz",        no_argument,       NULL, OPT_SYSTZ      },
                { "predict",      no_argument,       NULL, OPT_PREDICT    },
                { "get",          no_argument,       NULL, OPT_GET        },
                { "update-drift", no_argument,       NULL, OPT_UPDATE     },
                { NULL, 0, NULL, 0 }
        };

        static const ul_excl_t excl[] = {       /* rows and cols in ASCII order */
                { 'a','r','s','w',
                  OPT_GET, OPT_GETEPOCH, OPT_PREDICT,
                  OPT_SET, OPT_SETEPOCH, OPT_SYSTZ },
                { 'l', 'u' },
                { OPT_ADJFILE, OPT_NOADJFILE },
                { OPT_NOADJFILE, OPT_UPDATE },
                { 0 }
        };
        int excl_st[ARRAY_SIZE(excl)] = UL_EXCL_STATUS_INIT;

        /* Remember what time we were invoked */
        gettimeofday(&startup_time, NULL);

#ifdef HAVE_LIBAUDIT
        hwaudit_fd = audit_open();
        if (hwaudit_fd < 0 && !(errno == EINVAL || errno == EPROTONOSUPPORT ||
                                errno == EAFNOSUPPORT)) {
                /*
                 * You get these error codes only when the kernel doesn't
                 * have audit compiled in.
                 */
                warnx(_("Unable to connect to audit system"));
                return EXIT_FAILURE;
        }
#endif
        setlocale(LC_ALL, "");
#ifdef LC_NUMERIC
        /*
         * We need LC_CTYPE and LC_TIME and LC_MESSAGES, but must avoid
         * LC_NUMERIC since it gives problems when we write to /etc/adjtime.
         *  - gqueri@mail.dotcom.fr
         */
        setlocale(LC_NUMERIC, "C");
#endif
        bindtextdomain(PACKAGE, LOCALEDIR);
        textdomain(PACKAGE);
        atexit(close_stdout);

        while ((c = getopt_long(argc, argv,
                                "hvVDalrsuwf:", longopts, NULL)) != -1) {

                err_exclusive_options(c, longopts, excl, excl_st);

                switch (c) {
                case 'D':
                        ctl.debug++;
                        break;
                case 'a':
                        ctl.adjust = 1;
                        ctl.show = 0;
                        ctl.hwaudit_on = 1;
                        break;
                case 'l':
                        ctl.local_opt = 1;      /* --localtime */
                        break;
                case 'r':
                        ctl.show = 1;
                        break;
                case 's':
                        ctl.hctosys = 1;
                        ctl.show = 0;
                        ctl.hwaudit_on = 1;
                        break;
                case 'u':
                        ctl.utc = 1;
                        break;
                case 'w':
                        ctl.systohc = 1;
                        ctl.show = 0;
                        ctl.hwaudit_on = 1;
                        break;
                case OPT_SET:
                        ctl.set = 1;
                        ctl.show = 0;
                        ctl.hwaudit_on = 1;
                        break;
#if defined(__linux__) && defined(__alpha__)
                case OPT_GETEPOCH:
                        ctl.getepoch = 1;
                        ctl.show = 0;
                        break;
                case OPT_SETEPOCH:
                        ctl.setepoch = 1;
                        ctl.show = 0;
                        ctl.hwaudit_on = 1;
                        break;
                case OPT_EPOCH:
                        ctl.epoch_option = optarg;      /* --epoch */
                        break;
#endif
                case OPT_NOADJFILE:
                        ctl.noadjfile = 1;
                        break;
                case OPT_DIRECTISA:
                        ctl.directisa = 1;
                        break;
                case OPT_TEST:
                        ctl.testing = 1;        /* --test */
                        break;
                case OPT_DATE:
                        ctl.date_opt = optarg;  /* --date */
                        break;
                case OPT_ADJFILE:
                        ctl.adj_file_name = optarg;     /* --adjfile */
                        break;
                case OPT_SYSTZ:
                        ctl.systz = 1;          /* --systz */
                        ctl.show = 0;
                        ctl.hwaudit_on = 1;
                        break;
                case OPT_PREDICT:
                        ctl.predict = 1;        /* --predict */
                        ctl.show = 0;
                        break;
                case OPT_GET:
                        ctl.get = 1;            /* --get */
                        ctl.show = 0;
                        break;
                case OPT_UPDATE:
                        ctl.update = 1;         /* --update-drift */
                        break;
#ifdef __linux__
                case 'f':
                        ctl.rtc_dev_name = optarg;      /* --rtc */
                        break;
#endif
                case 'v':                       /* --version */
                case 'V':
                        out_version();
                        return 0;
                case 'h':                       /* --help */
                        usage();
                default:
                        errtryhelp(EXIT_FAILURE);
                }
        }

        if (argc -= optind) {
                warnx(_("%d too many arguments given"), argc);
                errtryhelp(EXIT_FAILURE);
        }

        if (!ctl.adj_file_name)
                ctl.adj_file_name = _PATH_ADJTIME;

        if (ctl.update && !ctl.set && !ctl.systohc) {
                warnx(_("--update-drift requires --set or --systohc"));
                exit(EXIT_FAILURE);
        }

        if (ctl.noadjfile && !ctl.utc && !ctl.local_opt) {
                warnx(_("With --noadjfile, you must specify "
                        "either --utc or --localtime"));
                exit(EXIT_FAILURE);
        }

        if (ctl.set || ctl.predict) {
                if (!ctl.date_opt) {
                warnx(_("--date is required for --set or --predict"));
                exit(EXIT_FAILURE);
                }
                if (parse_date(&when, ctl.date_opt, NULL))
                        set_time = when.tv_sec;
                else {
                        warnx(_("invalid date '%s'"), ctl.date_opt);
                        exit(EXIT_FAILURE);
                }
        }

#if defined(__linux__) && defined(__alpha__)
        if (ctl.getepoch || ctl.setepoch) {
                manipulate_epoch(&ctl);
                hwclock_exit(&ctl, EXIT_SUCCESS);
        }
#endif

        if (ctl.debug) {
                out_version();
                printf(_("System Time: %ld.%06ld\n"),
                       startup_time.tv_sec, startup_time.tv_usec);
        }

        if (!ctl.systz && !ctl.predict)
                determine_clock_access_method(&ctl);

        if (!ctl.noadjfile && !(ctl.systz && (ctl.utc || ctl.local_opt))) {
                if ((rc = read_adjtime(&ctl, &adjtime)) != 0)
                        hwclock_exit(&ctl, rc);
        } else
                /* Avoid writing adjtime file if we don't have to. */
                adjtime.dirty = 0;
        ctl.universal = hw_clock_is_utc(&ctl, adjtime);
        rc = manipulate_clock(&ctl, set_time, startup_time, &adjtime);
        hwclock_exit(&ctl, rc);
        return rc;              /* Not reached */
}

void
hwclock_exit(const struct hwclock_control *ctl
#ifndef HAVE_LIBAUDIT
             __attribute__((__unused__))
#endif
             , int status)
{
#ifdef HAVE_LIBAUDIT
        if (ctl->hwaudit_on && !ctl->testing) {
                audit_log_user_message(hwaudit_fd, AUDIT_USYS_CONFIG,
                                       "op=change-system-time", NULL, NULL, NULL,
                                       status);
        }
        close(hwaudit_fd);
#endif
        exit(status);
}

/*
 * History of this program:
 *
 * 98.08.12 BJH Version 2.4
 *
 * Don't use century byte from Hardware Clock. Add comments telling why.
 *
 * 98.06.20 BJH Version 2.3.
 *
 * Make --hctosys set the kernel timezone from TZ environment variable
 * and/or /usr/lib/zoneinfo. From Klaus Ripke (klaus@ripke.com).
 *
 * 98.03.05 BJH. Version 2.2.
 *
 * Add --getepoch and --setepoch.
 *
 * Fix some word length things so it works on Alpha.
 *
 * Make it work when /dev/rtc doesn't have the interrupt functions. In this
 * case, busywait for the top of a second instead of blocking and waiting
 * for the update complete interrupt.
 *
 * Fix a bunch of bugs too numerous to mention.
 *
 * 97.06.01: BJH. Version 2.1. Read and write the century byte (Byte 50) of
 * the ISA Hardware Clock when using direct ISA I/O. Problem discovered by
 * job (jei@iclnl.icl.nl).
 *
 * Use the rtc clock access method in preference to the KDGHWCLK method.
 * Problem discovered by Andreas Schwab <schwab@LS5.informatik.uni-dortmund.de>.
 *
 * November 1996: Version 2.0.1. Modifications by Nicolai Langfeldt
 * (janl@math.uio.no) to make it compile on linux 1.2 machines as well as
 * more recent versions of the kernel. Introduced the NO_CLOCK access method
 * and wrote feature test code to detect absence of rtc headers.
 *
 ***************************************************************************
 * Maintenance notes
 *
 * To compile this, you must use GNU compiler optimization (-O option) in
 * order to make the "extern inline" functions from asm/io.h (inb(), etc.)
 * compile. If you don't optimize, which means the compiler will generate no
 * inline functions, the references to these functions in this program will
 * be compiled as external references. Since you probably won't be linking
 * with any functions by these names, you will have unresolved external
 * references when you link.
 *
 * Here's some info on how we must deal with the time that elapses while
 * this program runs: There are two major delays as we run:
 *
 *      1) Waiting up to 1 second for a transition of the Hardware Clock so
 *         we are synchronized to the Hardware Clock.
 *      2) Running the "date" program to interpret the value of our --date
 *         option.
 *
 * Reading the /etc/adjtime file is the next biggest source of delay and
 * uncertainty.
 *
 * The user wants to know what time it was at the moment he invoked us, not
 * some arbitrary time later. And in setting the clock, he is giving us the
 * time at the moment we are invoked, so if we set the clock some time
 * later, we have to add some time to that.
 *
 * So we check the system time as soon as we start up, then run "date" and
 * do file I/O if necessary, then wait to synchronize with a Hardware Clock
 * edge, then check the system time again to see how much time we spent. We
 * immediately read the clock then and (if appropriate) report that time,
 * and additionally, the delay we measured.
 *
 * If we're setting the clock to a time given by the user, we wait some more
 * so that the total delay is an integral number of seconds, then set the
 * Hardware Clock to the time the user requested plus that integral number
 * of seconds. N.B. The Hardware Clock can only be set in integral seconds.
 *
 * If we're setting the clock to the system clock value, we wait for the
 * system clock to reach the top of a second, and then set the Hardware
 * Clock to the system clock's value.
 *
 * Here's an interesting point about setting the Hardware Clock:  On my
 * machine, when you set it, it sets to that precise time. But one can
 * imagine another clock whose update oscillator marches on a steady one
 * second period, so updating the clock between any two oscillator ticks is
 * the same as updating it right at the earlier tick. To avoid any
 * complications that might cause, we set the clock as soon as possible
 * after an oscillator tick.
 *
 * About synchronizing to the Hardware Clock when reading the time: The
 * precision of the Hardware Clock counters themselves is one second. You
 * can't read the counters and find out that is 12:01:02.5. But if you
 * consider the location in time of the counter's ticks as part of its
 * value, then its precision is as infinite as time is continuous! What I'm
 * saying is this: To find out the _exact_ time in the hardware clock, we
 * wait until the next clock tick (the next time the second counter changes)
 * and measure how long we had to wait. We then read the value of the clock
 * counters and subtract the wait time and we know precisely what time it
 * was when we set out to query the time.
 *
 * hwclock uses this method, and considers the Hardware Clock to have
 * infinite precision.
 */